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F. H. ROYCE. ELECTRIC CONTACT BREAKER. APPLICATION FILED MAY 6. 1918.

Inre ntor- Frederick HenryRoyce UNITED STATES PATENT OFFICE.

FREDERICK HENRY BOYCE, 0F DERBY, ENGLAND, ASSIGNOR TO ROLLS-ROYCE LIMITED, 0F DERBY, ENGLAND.

ELECTRIC CONTACT-BREAKER.

Specification of Letters Patent.

Patented Aug. 17, 1920.

Application filed May 6, 1918. Serial No. 232,822.

T 0 all whom it may concern Be it known that I, FREDERICK HENRY RoYcn, of Derby, in the county of Derby, England, have invented certain new and use ful Improvements in Electric Contact- Breakers, of which the following is a specification.

This invention comprises an improved contact breaker or interrupter for breaking or interrupting the low tension circuits in connection with the magnetos of internal combustion engines and has for its object to provide a more reliable mechanism than has heretofore been in vogue, and one which is capable of operating correctly at a high rate of revolution of said engine.

In many forms of contact breakers hitherto proposed or in use the frame carrying the mechanism rotates within an annular cam and a rocking lever is used one arm of which is acted upon by the cam and the other arm carrying a movable contact piece the construction being such that the action of the cam breaks contact while the return of the lever to make contact is effected wholly by a spring or partly by a spring and partly by centrifugal force. In such mechanisms the moving part or parts which have been given comparatively large weight have been subjected, on every lift of the cam, to a very rapid acceleration by reason of the required shape of the cam, resulting in a high value for the force of inertia of such parts. It has been found that at moderately high speeds of such mechanisms this force of inertia overcomes the spring or centrifugal force employed to reverse the movement of the lever and that at very high speeds the said force causes breakage of the lever and the spring.

In the present invention the mechanism carrying the moving contact piece and actuating it to make contact is separate from the rocking arm, which merely operates on it to break contact. By thus separating the parts the mechanism to break contact and the mechanism to make contact can be separately designed and controlled with a view to reducing to a minimum and more readily overcoming the said force of inertia and means are provided to this end accordingly. For example the said force of inertia of the moving parts of the mechanism making contact is reduced by reducing the mass or weight of such parts to a minimum and the said force of inertia of the rocking lever is more readily overcome firstly by actuating it by a cam of which the eccentricity is very slight and the approach very long and gradual, the ratio of approach to eccentricity being relatively high, and the shape of the cam being preferably such as to give a smooth and harmonious motion to the lever, and secondly by insuring that the mass of the lever itself is so formed and poised in relation to its fulcrum that it is kept constantly in. contact with the cam by centrifugal force.

In the accompanying drawings there is illustrated an example of the invention,

Figure 1 being an end view of the mechanism and Fig. 2 a cross section on the line D-D of Fig. 1 with the cam removed.

a designates the rotating frame which carri'es the mechanism, Z) the lever rocking on the stud one arm of which lever carries the fiber block b and the other arm of which carries the fiber block 6 0 designates the operating surface of the fixed cam, its eccentric shape being indicated by the broken line 0 which shows a true circle from the center 0; (Z indicates a leaf spring anchored to the frame a by means of the bracket (Z and screw (Z and carrying the moving contact e which is riveted to the spring (Z, f is a bracket supported on the frame a and carrying the contact shaft r and the adjustable screw contact piece h which carries the fixed platinum contact 5. The screw contact h is hollowed to enable the contact 2' to be riveted as shown at 11 l: is a screw to clamp the bracket f (which is split) and lock the screw h in said bracket while Z is an extension of the bracket 7 and Z a bolt for holding the bracket to the frame a. m is insulating material between the bracket and rotating frame a and around the shaft 9.

The mass of the lever 7) is so arranged and the lever is so poised about the stud b that the fiber block Z) is kept in constant contact with the face of the cam 0 by centrifugal force.

The electric circuit is made through the frame a the spring (5 the moving and fixed contacts 6 and i respectively and the central shaft g.

In action, the lever Z acts on the spring (l to tension same and force back the moving contact piece a to break the contact and then releases said contact piece to enable it under the influence of the spring d to remake the contact.

Giving to the shape of the cam c the acceleration of the lever b is reduced to a small amount and owing to the arrangement of the mass and the poise of said lever in relation to its bearing stud the centrifugal force op erating on the mass of the lever is powerful enough to overcome the aforesaid force of inertia with the result that the lever is kept in engagement with the cam at all speeds.

Owing to the comparatively small mass of the moving contact and spring their inertia is also small and although the acceleration may be rapid the spring can readily overcome forces of inertia.

As a result of the construction described the causes of failure in such instruments as heretofore in use are removed.

W hat I claim as my invention and desire to secure by Letters'Patent of the United States is A. contact breaker for the magnetos of internal combustion engines, comprising in combination a stationary cam having a very slight eccentricity and a long and very gradual approach, the ratio of approach to eccentricity being relatively high; a frame rotatable within the cam; a double-armed rocking lever carried by said frame and actuated by said cam to receive a harmonious and smooth motion, one arm of said lever being maintained in constant contact with said cam by centrifugal force alone; a spring mounted on the frame independently of the cam and rocking lever; and a movable contact carried by the spring, the second arm of the rocking lever freely contacting with said spring so that on rotation of the frame in relation to the cam, the spring isalternately put in tension by the rocking lever to cause the movable contact to break circuit and released to remake said circuit under the action or" the spring; the aforesaid disposition of the elements permitting forces of inertia in the contact mechanism to be reduced to a minimum and readily overcome, while allowing high rotational speed of the frame.

In witness whereof I have signed this specification in the presence of two witnesses.

FREDERICK HENRY ROYCE.

Vitnesses H. R. CUr'rEN,

F. PARsoNs. 

